Coupled transponder and antenna system and method

ABSTRACT

Annular apparatus comprises a toroidal body composed of a material having high electromagnetic permeability and the body a through bore; an electrical device coupled to the toroidal body; and a loop antenna disposed to extend through the through bore in direct magnetic coupled relationship with the toroidal body. The loop antenna is in a mechanically de-coupled relationship with the toroidal body and lies substantially in a first plane that intersects the toroidal body opening at a right angle. In one embodiment, the electrical device comprises a transponder for monitoring cavity parameters in a pneumatic tire.

FIELD OF THE INVENTION

[0001] The invention relates generally to the coupling of electronic devices such as a transponder and antenna and, more specifically, to direct magnetic coupling of a transponder and annular antenna for use in pneumatic tires.

BACKGROUND OF THE INVENTION

[0002] This invention relates to an annular apparatus, including an antenna for electronically transmitting tire or wheel identification or other data at radio frequency. The apparatus includes a radio-frequency transponder comprising an integrated circuit chip having data capacity at least sufficient to retain identification information for the tire or wheel. Other data, such as the inflation pressure of the tire or the temperature of the tire or wheel at the transponder location, can be transmitted by the transponder along with the identification data. While the subject invention is specifically directed to the coupling of a transponder to an antenna for use in pneumatic tires, the invention is not so restricted. The principles herein described may find application in the magnetic coupling of a range of electronic devices to an annular antenna for myriad other applications that will be apparent to those in the art.

[0003] As is evidenced by the references described below, it is known in the art to employ an annular antenna to transmit, at radio frequencies, data from a transponder contained within the structure of a tire or tire and wheel assembly. In practice, however, it is very difficult to do this with an antenna incorporated into the tire during the course of its manufacture. Both radial ply and bias ply tires undergo a substantial diametric enlargement during the course of manufacture. Bias ply tires are expanded diametrically when inserted into a curing press, which typically has a bladder that forces the green tire into the toroidal shape of the mold enclosing it. Radial ply tires undergo diametric expansion during the tire building or shaping process and a further diametric expansion during the course of curing. Any annular antenna and the electronic circuitry associated therewith built into the tire must be able to maintain structural integrity during the diametric enlargement of the tire during its manufacture. Furthermore, the annular antenna must be able to survive the repeated deformations occurring during tire use and the rigors imparted by testing procedures to which tires are subjected before retreading. Accordingly, a need exists for an annular apparatus and method sufficient to maintain mechanical and structural integrity in the transponder-antenna loop connection during the diametric enlargement of the tire during the building and curing process. In addition, the antenna and the transponder-antenna loop connection must be durable and able to maintain structural integrity throughout the rigors of tire operation and retreading procedures without degradation in performance or malfunction due to breakage of wire or electrical connections.

[0004] Beyond the need to maintain mechanical structural integrity as discussed above, it is important that the connection between the antenna and the transponder provide a high energy transfer. Passive transponders require that energy be supplied from a remote (non-contact) source of energy. This energy coupling is commonly achieved by generating an LF (for example 125 kHz to 135 kHz) alternating current in a reader antenna coil. The reader coil is typically, but not necessarily, a series resonant Inductive-Capacitive (LC) circuit. The current in the reader antenna coil creates a nearby magnetic field. A passive transponder within this field captures energy by inductive coupling between the magnetic field and the transponder antenna coil, which is typically, but not necessarily, incorporated into a parallel tuned resonant LC circuit.

[0005] One form of transponder antenna coil is a large diameter wire loop of one or a very few turns. Such an antenna is very useful in a tire, for example, where the loop can be deployed in the tire crown or sidewall to provide a continuous coupling through 360 degrees of rotation. A large loop of one or a few turns offers a large area to capture energy from the field of the reader antenna coil, but has very low inductance. A poor quality resonant LC circuit and poor impedance matching to the transponder electronics results. To overcome poor impedance matching, a transformer may be employed, consisting of a low number of primary turns in series with the loop antenna and a high number of secondary turns connected to the input of the transponder electronics. The transformer provides a higher inductance on the primary side and therefore enables a high quality tuned LC circuit, a high voltage level at the transponder input, and good impedance matching to the transponder electronics. The most efficient means of creating such a transformer is by using a ferrite material, typically in a toroidal configuration, to yield a high efficiency and high coupling factor in a small volume.

[0006] The connection between the large diameter antenna loop and the fine wire used in the primary winding of a toroidal transformer can, however, be problematic in a transponder package. The antenna loop is often a stiff and strong material to meet the requirements of a particular application such as tires. Electrical connection between the stiff wire and the fine wire creates reliability and process problems. The material composition of the loop antenna may not permit soldering and the small space available may make establishing a strong mechanical connection difficult. Additionally, terminating a stiff wire in the small volume available in transponder packages may result in a weak and less than durable terminal junction. As a result, stress imposed on the connection from flexing or other movement of the loop antenna may cause the connection to fail. Moreover, in a typical transponder package, only a small amount of epoxy or other encapsulant material is available to resist such stress.

[0007] It is known in the art to position a transponder with a wound ferrite rod near a long wire loop. Current induced in the loop from the reader creates a magnetic field near the loop that is coupled into the rod. Other alternate known embodiments take a portion of the long loop and wind it into a small area “concentrator” winding. The concentrator winding concentrates the magnetic field and causes more inductive coupling to a ferrite rod transponder antenna placed proximate the winding. Electrically such a connection represents a loosely coupled transformer where the concentrator winding is the primary of the transformer and the winding on the ferrite rod is the secondary winding.

[0008] One problem inherent in incorporating such known antenna-transponder assemblies into tire based systems is caused when the transponder transformer passes directly under the reader antenna once every rotation. If the transformer primary winding is magnetically open, as in the case of a ferrite rod, the magnetic field from the reader induces current in the secondary winding directly, counteracting the current induced from the antenna loop. This direct coupling is in reverse phase to the loop coupling. Consequently, at two spots in each rotation the two fields exactly counteract, causing a null in the coupling. This occurrence eliminates a preferable 360 degree read and can prevent reading transponders at high wheel speeds. It is accordingly, a need to provide an antenna-transponder assembly for tire systems that provides a continuous 360 degree read, a high coupling factor, and minimal interference between current induced by the reader magnetic field and that induced from the antenna loop.

[0009] U.S. Pat. No. 5,181,975 discloses a pneumatic tire having an integrated circuit (IC) transponder and pressure transducer. As described in this patent, the transponder may be attached to an inner surface of the tire by means of a tire patch or other similar material or device. U.S. Pat. No. 5,541,574 discloses an annular antenna lodged within a groove that extends around a tube. U.S. Pat. No. 4,319,220 discloses a system for monitoring tire pressure comprising wheel units in the tires and a common receiver. Each wheel unit has an antenna comprising a continuous wire loop embedded in an open annulus which is disposed against the inner periphery of the tire for transmitting signals and for receiving power. U.S. Pat. No. 6,147,659 discloses the use of metallic component members in a tire as an antenna directly connected to a transponder. U.S. Pat. No. 4,074,227 discloses a tire pressure indicator for a tire and includes a transponder coupled to a signal coil that is disposed as a circular loop about the tire. U.S. Pat. No. 5,491,483 discloses a single loop annular antenna mechanically and magnetically coupled to a transponder through an impedance transformer.

[0010] While the prior art listed above functions well and represents several viable approaches toward meeting the needs of the industry, certain deficiencies inherent in each prevent the collective prior art from achieving a satisfactory system, assembly, and method for magnetically coupling an annular antenna to a transponder. The prior art either provides a less than satisfactory coupling factor; a less than durable transponder to loop connection; a complicated method of attaching the antenna loop to a transponder; or a relatively high system cost. Consequently, the industry remains in need of a system, assembly, and method for achieving a high annular antenna to transponder magnetic coupling while mechanically isolating the antenna from the transponder. Heretofore, a system providing an annular antenna that is magnetically coupled to but mechanically de-coupled from a transponder has not been attained. Additionally, a satisfactory system will comprise relatively inexpensive components that facilitate easy and inexpensive manufacture and assembly. Moreover, a satisfactory system will be durable and capable of withstanding the stress described above that is attendant many applications for the system including tires.

SUMMARY OF THE INVENTION

[0011] The subject invention overcomes the deficiencies in known systems and methods for coupling an annular antenna to an electrical device such as a transponder. A toroidal body is formed from material having a high electromagnetic permeability. No primary winding is used in conjunction with or as part of the toroidal device. Rather, the antenna loop is passed directly through the center opening in the toroid and couples magnetically with the toroidal body absent a primary winding. Magnetic coupling occurs between the loop and the toroid, and therefore into the secondary winding because the current induced in the loop antenna from the transceiver magnetic field creates a magnetic field near the loop. The magnetic field is induced directly into the ferrite toroid that closely surrounds the loop wire(s). Such a coupling is hereinafter designated as Direct Magnetic Coupling (DMC). The DMC approach allows the antenna loop to pass through the transponder package without a mechanical connection and therefore eliminates the problems with making and maintaining the connection between the loop wire and the transponder package discussed previously. The secondary turn ratio may be varied to accommodate optimum impedance matching. Consequently, the DMC technique provides a high energy coupling and high durability since external connection between the antenna loop and the toroidal body is eliminated. Furthermore, the process of attaching the antenna loop to a transponder is simplified rendering any remote coupling between wire bundles or cables and transponders substantially less difficult. Moreover, the magnetic coupling between annular antenna and transponder using the DMC technique is maintained in a continuous 360 degree read and dead zones in the interrogation area are avoided.

[0012] According to another aspect of the invention, the antenna and the transponder are at least partially embedded into a non-conductive encapsulant material to render the antenna and transponder package unitarily transportable. Such an assembly facilitates ease of incorporation of the assembly into a tire during the tire manufacturing process or in a post-manufacture attachment procedure. Moreover, the encapsulant material further serves to maintain the antenna and the toroidal body in mechanically decoupled yet electromagnetically coupled advantageous relationship.

[0013] According to a further aspect of the invention, a method is provided for associating a loop antenna with an electronic device such as a transponder through a toroidal body having a central opening. The method comprises the steps of positioning the loop antenna to project through the central opening in non-contacting relationship with the toroidal body; establishing a direct magnetic coupling between the loop antenna and the toroidal body; and coupling the electronic device to the antenna through the toroidal body. A further aspect of the invention is to include the steps of at least partially encapsulating the antenna and the electronic device package in a non-conductive material so as to render the antenna and the electronic device package unitarily transportable and to fix the relative position between the antenna and the electronic device in a specified orientation.

[0014] These and other aspects of the invention, which will be apparent to those skilled in the art, are achieved by preferred and alternative embodiments that are described in detail below and illustrated by the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a perspective view of a tire and the subject annular apparatus with portions of the tire removed for the purpose of illustration.

[0016]FIG. 2 is a sectional schematic of a tire mounted to a rim and illustrating alternative locations in which to mount the subject annular apparatus.

[0017]FIG. 3 is an enlarged perspective view of a tire portion having a transponder and antenna assembly positioned against a tire sidewall surface.

[0018]FIG. 4 is a sectional schematic view of a tire and wheel assembly mounted to a vehicle frame.

[0019]FIG. 5 is an enlarged perspective view of the subject antenna projecting through a transponder module.

[0020]FIG. 6 is an enlarged perspective view of a portion of the subject annular assembly.

[0021]FIG. 7 is a front perspective view of the subject transponder module.

[0022]FIG. 8 is an exploded perspective view thereof.

[0023]FIG. 9 is a top plan view thereof

[0024]FIG. 10 is a longitudinal section view through the transponder module of FIG. 9 taken along the line 10-10.

[0025]FIG. 11 is a transverse section view through the transponder module of FIG. 9 taken along the line 11-11.

[0026]FIG. 12 is a perspective view of the module circuit board.

[0027]FIG. 13 is a perspective view of the receiver module.

[0028]FIG. 14 is a perspective view of an alternative embodiment of the transponder module.

[0029]FIG. 15 is a block diagram of the car transceiver and tire monitoring system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] As used herein, a “transponder” is an electronic apparatus (device) capable of monitoring a condition such as air pressure within a pneumatic tire, and then transmitting that information to an external device. The external device can be either an RF (radio frequency) reader/interrogator or, simply an RF receiver. A simple receiver can be used when the transponder is “active”, and has its own power source. A reader/interrogator would be used when the transponder is “passive” and is powered by an RF signal from the reader/interrogator. In either case, in conjunction with the external device, the transponder forms a component of an overall tire-condition monitoring/warning system. A “ferrite toroid” is coupled to the transponder by a secondary winding.

[0031] As used herein, a “ferrite toroid” is a toroidal body formed from ferro-magnetic material by a continuous curved surface and including a central through opening. The toroidal body may be cylindrical, oblong, symmetrical, or asymmetrical without departing from the invention herein set forth. In order to send or receive RF signals, a transponder must have an antenna. This antenna is annular in configuration and may either be incorporated into the tire during manufacture or affixed to the tire by way of a post manufacture procedure. The antenna may comprise a single wire or a plurality of strands. Various commercially available transponders, sensors, and other electrical devices deployed in combination with an annular antenna are suitable for use in conformance with the principles of the subject invention 

What is claimed is:
 1. An apparatus comprising: a toroidal body composed of a material having high electromagnetic permeability and the body having a through bore, an electrical device coupled to the toroidal body, a loop antenna disposed to extend through the through bore in direct magnetic coupled relationship with the toroidal body.
 2. An apparatus according to claim 1, wherein the loop antenna is in mechanically de-coupled relationship with the toroidal body.
 3. An apparatus according to claim 1 wherein the loop antenna lies substantially in a first plane that intersects the toroidal body opening at a substantially right angle.
 4. An apparatus according to claim 1, wherein the electrical device comprises a transponder.
 5. An apparatus according to claim 1, wherein the loop antenna comprises at least one wire.
 6. An annular apparatus comprising: a toroidal body composed of a material having high electromagnetic permeability and the body having a through bore; a transponder coupled to the toroidal body; a loop antenna disposed to extend through the through bore in a magnetically coupled relationship and a mechanically de-coupled relationship with the toroidal body.
 7. An apparatus according to claim 6, wherein the loop antenna lies substantially in a first plane that intersects the toroidal body opening at a substantially right angle.
 8. An apparatus according to claim 6, wherein the loop antenna comprises at least one wire formed into a substantially sinusoidal wave conformation.
 9. An apparatus according to claim 6, wherein the transponder and the toroidal body reside within a common housing.
 10. In an apparatus of the type comprising a toroidal body composed of material having high electromagnetic permeability and the body having a through bore; a transponder coupled to the toroidal body, and a loop antenna magnetically coupled to the transponder through the toroidal body, characterized in that the loop antenna extends through the central opening in a non-contacting and mechanically decoupled relationship with the toroidal body.
 11. An apparatus according to claim 10, wherein the loop antenna lies within a first plane normally disposed to the toroidal body through bore.
 12. An apparatus according to claim 10, wherein the loop antenna is in direct magnetically coupled relationship and mechanically de-coupled relationship with the toroidal body.
 13. An apparatus according to claim 10, further characterized as including a housing in which the toroidal body and the transponder commonly reside.
 14. A method of associating a loop antenna with an electronic device through a toroidal body composed of a material of high elector-magnetic permeability and the body having a through bore, comprising the steps of: positioning the loop antenna to project through the through bore in non-contacting and mechanically decoupled relationship with the toroidal body, establishing a direct magnetic coupling between the loop antenna and the toroidal body, and coupling the electronic device to the antenna through the toroidal body.
 15. A method as set forth in claim 14, further comprising the step of orienting the loop antenna to lie within a first plane normally disposed to the toroidal body through bore.
 16. A method according to claim 14, further comprising the step of locating the toroidal body and the electronic device within a common housing.
 17. A method of associating a loop antenna with an electronic device through a toroidal body composed of a material of high electromagnetic permeability and the body having a central opening, comprising the steps of: establishing a magnetic coupling between the loop antenna and the toroidal body; coupling the electronic device to the antenna through the toroidal body; embedding at least a portion of the antenna loop and at least a portion of the electronic device in an electrically non-conductive encapsulant material to maintain the antenna loop and the toroidal body in a specified orientation.
 18. A method according to claim 17, further comprising the step of extending the antenna through the toroidal body through bore in a mechanically decoupled relationship therewith.
 19. A method according to claim 18, further comprising the steps of: positioning the toroidal body in an orientation in which the antenna intersects the, through bore at substantially a right angle; and employing the encapsulant material to maintain the toroidal body in said orientation.
 20. A method according to claim 17, further comprising the step of employing the encapsulant material to render the toroidal body and the electronic device unitarily transportable. 